1. Field of the Invention
The present invention relates to an electron bean writing method and a fine pattern writing system for writing a fine pattern according to a desired uneven pattern when manufacturing an imprint mold, magnetic transfer master substrate, or the like for a high density magnetic recording medium, such as a discrete track medium, bit pattern medium, or the like.
The present invention also relates to a method for manufacturing an uneven pattern carrying substrate that includes an imprint mold, magnetic transfer master substrate, or the like having an uneven pattern surface formed through a writing step performed by the electron beam writing method described above. The invention further relates to a method for manufacturing a magnetic disk medium having an uneven pattern transferred thereto from the uneven pattern carrying substrate or imprint mold, and a method for manufacturing a magnetic disk medium having a magnetized pattern transferred thereto from the magnetic transfer master substrate.
2. Description of the Related Art
Generally, information patterns, such as servo patterns and the like are formed on a current magnetic disk medium. In view of the demand of higher recording density, a discrete track medium (DTM) in which magnetic interference between adjacent data tracks is reduced by separating the tracks with a groove pattern (guard band) has been attracting wide attention. A bit pattern medium (BPM) proposed for achieving still higher density is a medium in which magnetic substances forming single magnetic domains (single-domain particles) are physically isolated and disposed regularly, and one bit is recorded in a single particle.
Heretofore, fine patterns, such as servo patterns and the like, have been formed on magnetic media by uneven patterns, magnetic patterns, or the like, and an electron beam writing methods for patterning a predetermined fine pattern on a master of a magnetic transfer master substrate or the like have been proposed. In the electron beam writing methods, a pattern is written on a substrate applied with a resist by irradiating thereon an electron beam corresponding to the shape of the pattern while rotating the substrate as described, for example, in U.S. Pat. No. 7,026,098 and Japanese Unexamined Patent Publication No. 2006-184924.
The electron beam writing method described in U.S. Pat. No. 7,026,098 is a method in which when, for example, writing a rectangular or parallelogram element constituting a servo pattern extending in the width direction of a track, the electron beam is deflected in a radius direction while being vibrated rapidly in circumferential directions to scan the beam so as to completely fill the area of the element.
The electron beam writing method described in Japanese Unexamined Patent Publication No. 2006-184924 is a method in which the electron beam is vibrated in the track width directions of the pattern.
Further, a method in which an electron beam is on/off irradiated on a substrate applied with a resist according to the shape of a pattern while the substrate is rotated, and the substrate or the electron beam irradiation device is moved by a single beam width in a radius direction per one revolution is also known as an on/off writing method.
In the writing methods described in U.S. Pat. No. 7,026,098 and Japanese Unexamined Patent Publication No. 2006-184924, patterns on one track are written by one revolution of the substrate by rapidly vibrating the electron beam in the circumferential directions or radius directions of the substrate, thereby reducing the time required for pattern writing over the entire surface of the substrate.
In the mean time, when writing fine patterns by the electron beam writing methods described above, it is difficult to accurately write elements which form each pattern over the entire tracks from the innermost circumferential track to the outermost circumferential track with a uniform amount (dose amount) of radiation exposure.
In particular, for those that vibrate the electron beam in the radius or circumferential directions, it is difficult write a pattern which includes elements having different lengths in the radius directions (track width directions) or circumferential directions (track directions) with a uniform amount of radiation exposure.
The reason is that the change in the beam intensity of the electron beam causes beam instability so that the beam intensity can not be changed during the writing of elements according to the shapes of the elements. Consequently, the writing is performed with an optimum amount of radiation exposure by equalizing the writing area per unit time to adjust to the sensitivity of the resist.
That is, the electron beam writing is a method in which a substrate is placed on a rotation stage and, while the substrate is rotated at a constant speed, an electron beam is scan controlled on the substrate, whereby elements on one track are sequentially written. For example, when writing a fine pattern of a discrete track medium, the writing can be performed over the entire surface of the substrate with a substantially uniform amount of radiation exposure for a servo pattern by controlling the rotational speed of the substrate so as to correspond to a change in the circumferential length of elements, since each of the elements of the servo pattern has a rectangular shape with substantially the same size. But, when writing the groove pattern for separating the adjacent track described above following the servo pattern, if the electron beam is fixedly irradiated to write the groove pattern in an arc shape by the rotation of the substrate, the electron beam intensity for the servo pattern writing is too intense for the groove writing since the groove pattern has a narrow width in the radius directions and continued in the track directions. Consequently, the line width becomes larger by exposure bleeding, thereby posing a problem that writing of a groove pattern having a predetermined width relative to the track width can not be performed. The emitted electron beam is subjected to deflection control so as to be vibrated, scanned to fill element areas, and moved between tracks. Such deflection control alone is insufficient for the flexibility in the change of radiation exposure amount and can not address the problem described above.
As described above, there is a demand for an electron beam writing method capable of highly accurately writing a fine pattern having a complicated shape both in an inner circumferential portion and an outer circumferential portion in response to the improvement of recording density of magnetic disk media.
The on/off writing method described above may write a pattern having a complicated shape by increasing the number of clocks in one rotation and improving positional accuracy. But, the method has a problem that it takes a lot of time to write a pattern over the entire substrate and it is difficult to perform pattern writing over the entire substrate by ensuring on/off positional accuracy of the electron beam according to the rotational position in inner and outer circumferences.
In view of the circumstances described above, it is an object of the present invention to provide an electron beam writing method capable of highly accurately writing a fine pattern having a complicated shape by further improving the flexibility to control the amount of radiation exposure in scan writing with an electron beam, and a fine pattern writing system for performing the electron beam writing method.
It is a further object of the present invention to provide a method for manufacturing an uneven pattern carrying substrate, such as an imprint mold or a magnetic transfer master substrate, having a fine pattern accurately written by an electron beam, and a method for manufacturing a magnetic disk medium having an uneven pattern or a magnetic pattern transferred thereto from the uneven pattern carrying substrate.